Chemical afferent vagal axotomy blocks re-intake after partial withdrawal of gastric food contents

Objectives: The aim of this study was to investigate the biological process by which animals regulate meal size. An experimental procedure for its study is to examine food re-intake after partial withdrawal of gastric food contents.

Methods: The aim of the present experiments was to investigate the role of vagal afferents in food re-intake after perivagal administration of capsaicin, a neurotoxin that specifically damages weakly myelinated or unmyelinated vagal sensory axons.

Results: In experiment 1, capsaicin-treated animals initially consumed higher amounts of food in comparison to controls (in first 24 hours) but their excess intake was compensated for in subsequent daily satiation tests. However, capsaicin treatment impaired the common short-term re-intake behavior observed in control rats after partial removal of gastric food nutrients, and the lesioned animals consumed significantly less food than had been withdrawn after completion of the initial meal; moreover, in this deficit condition, no counteraction was observed in subsequent repeated tests. This behavioral disturbance cannot be attributed to an indirect effect of capsaicin on gastric emptying volume, because the stomach contents were similar in both groups (Experiment 2).

Discussion: These findings are discussed in terms of the critical role played by vagal afferents in rapid visceral adjustments related to short-term food intake, as also observed in other gastrointestinal regulatory behaviors that require immediate processing of visceral sensory information.